CONTROLLED DEPOSITION OF STRONTIUM SULFATE ON BEHENIC ACID LANGMUIR-BLODGETT MULTILAYERS

As part of our on-going studies aimed at reaching an understanding of biologically controlled mineralization [1-3] the precipitation of strontium sulphate has been investigated in the presence of hydrophobic and hydrophilic behenic acid (CH3(CH2)20COOH) Langmuir-Blodgett (LB) films by electron microscopy and electron diffraction. The films exhibited most marked effects at low supersaturations and both nucleation and crystal growth processes were affected. In the absence of a film, tabular rhombic crystals are deposited with (001) forming the major growth face. Crystallization in the presence of hydrophobic films at low supersaturations (10 K(sp)) produces thin, disc-like crystals which are nucleated on the (010) crystal face of celestite. Hydrophilic substrates of 10 K(sp) and 30 K(sp) produce open-floret or needle shaped crystals, respectively, deposited on the films. The diffraction patterns obtained from these crystals cannot be assigned using the orthorhombic unit cell of celestite. At higher supersaturations, three-dimensional crystals of celestite based on symmetry related {011} and {210} faces are produced which show little contact with the film surface. Substrate-ion interactions are considered in order to understand the influence of the substrate on crystal nucleation. For precipitation in the presence of the hydrophobic film it is proposed that surface topography directly affects nucleation. For precipitates formed at low supersaturations in the presence of the hydrophilic film there is no direct surface: ion spatial correlation and deformed structures of celestite are observed.